Effects of Dietary Glutamine Supplementation on Heat-Induced Oxidative Stress in Broiler Chickens: A Systematic Review and Meta-Analysis

Systematic review and meta-analysis of experimental studies in heat-stressed broiler chickens. The included populations were mainly Arbor Acres and Ross 308 birds exposed to chronic, cyclic, or acute heat stress in China and Iran.

Dietary glutamine supplementation was administered in feed to heat-stressed broiler chickens across 13 experimental studies. The meta-analysis evaluated varying glutamine concentrations and supplementation durations rather than a single standardized dose.

Glutamine supplementation had an overall beneficial effect under heat stress, improving growth and antioxidant defenses in broiler chickens. Pooled results showed higher body weight gain (SMD = 0.70, CI = 0.50 to 0.90), higher feed intake (SMD = 0.64, CI = 0.43 to 0.86), and lower feed conversion ratio (MD = -0.05, CI = -0.07 to -0.02). Antioxidant markers also improved, including GPX (SMD = 1.12), SOD (SMD = 0.97), CAT (SMD = 0.94), GSH (SMD = 1.25), and tissue glutamine concentration (SMD = 1.21), while MDA decreased overall (SMD = -0.84). Benefits varied by tissue and exposure conditions: serum GPX was not significant (SMD = 0.45, p = 0.41), breast MDA was not significant (SMD = -0.38, p = 0.56), and longer heat exposure reduced the effect on feed intake, GPX, and SOD.

The evidence base was small and heterogeneous, with different heat-stress models, durations, tissues, and glutamine concentrations across studies. Several outcomes showed substantial between-study variability, and some effects were tissue-specific rather than uniform. Adverse events were not reported.